NAME:______________________________
CLASS:_______
Reading a Human Pedigree
Background:
Normal red blood cells are disc-shaped and look like doughnuts without holes in the center. They
move easily through your blood vessels. Red blood cells contain an iron-rich protein called hemoglobin
(HEE-muh-glow-bin). This protein carries oxygen from the lungs to the rest of the body.
Red blood cells are made in the bone marrow of larger bones of the body. Bone marrow is always
making new red blood cells to replace old ones. Normal red blood cells live about 120 days in the
bloodstream and then die. They carry oxygen and remove carbon dioxide (a waste product) from your
body.
Sickle cells contain abnormal hemoglobin called sickle hemoglobin or hemoglobin S. Sickle hemoglobin
causes the cells to develop a sickle, or crescent, shape. Sickle cells are stiff and sticky. They tend to
block blood flow in the blood vessels of the limbs and organs. Blocked blood flow can cause pain and
organ damage. It can also raise the risk for infection. In sickle cell anemia, the abnormal sickle cells
usually die after only about 10 to 20 days. The bone marrow can't make new red blood cells fast
enough to replace the dying ones.
Sickle cell anemia is an inherited, lifelong disease. People who have the disease are born with it. They
inherit two genes for sickle hemoglobin—one from each parent. People who inherit a sickle hemoglobin
gene from one parent and a normal gene from the other parent have a condition called sickle cell trait.
Sickle cell trait is different than sickle cell anemia. People who have sickle cell trait don't have the
disease. Like people who have sickle cell anemia, people who have sickle cell trait can pass the sickle
hemoglobin gene to their children.
Problem:
How can you use a human pedigree to trace the inheritance of sickle cell anemia through several
generations of a family?
Proceedure:
1. Study the following key for the symbols used on a human pedigree.
2. Study the pedigree shown here. The pedigree traces the pattern of inheritance of sickle cell
anemia in several generation of a single family.
NAME:______________________________
CLASS:_______
Observations:
1. How many generations are shown on the pedigree?
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2. Which parent in the first generation had sickle cell anemia?
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3. How many children were born in the second generation?
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4. How many children in the second generation had sickle cell anemia?
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5. How many children in the third generation have sickle cell anemia? How many are carriers?
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6. Is sickle cell anemia a sex linked trait? Ho can you tell?
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7. Is the gene for sickle cell dominant of recessive? How can you tell?
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